The specific objective of this research proposal is to assess qualitative and quantitative anatomical changes in area 17 of hooded rats visually deprived by neonatal binocular eyelid suture. Preliminary evidence suggests that the responses to this form of deprivation include: (1) an abnormal interlaminar projection of layer II/III neurons into layer IV, in addition to a redistribution of synaptic contacts by axon terminals in layer V from layer II/III neurons, and (2) a loss of layer II/III callosal neurons which project to the contralateral area 17/18 transition zone, and an expansion of layer V callosal neurons into area 17. Although the primary aim of this study is to characterize synaptic reorganization with layer IV, changes in commissural projections and the supragranular projection to layer V will be examined as well. Data obtained from light and electron microscopic investigations using degeneration, horseradish peroxidase, and autoradiographic methods will be analyzed using multivariate statistical techniques. Three groups of experiments are proposed: Group I experiments will examine those changes occurring in the geniculo-cortical projection to layer IV as a consequence of bilateral lid-sutre, and will assess: 1) whether there is a reduction in the number and/or density of axon terminals, 2) whether the distribution profile of post-synaptic contacts changes and, if so, in what way, 3) the relationship between changes in the geniculate projection to layer IV and the establishment of synapses within this layer by layer II/III neurons, 4) whether sprouting results in a greater than normal complement of synapses in layer IV, or 5) whether some degree of replacement occurs. Group II experiments will examine: 1) whether or not normal visual experience can induce a retraction of the synaptic contacts previously established in layer IV by supragranular neurons in response to lid-closure; and, 2) whether a critical period exists during which the supragranular projection is maximally responsive to restoration of visual experience. Group III experiments will examine alterations in callosal connections in lid-sutured rats as compared to the normal animal. This series of experiments should then provide further insights into the mechanisms by which formation of intracortical circuits is established, as well as their modification by altered sensory input.